The impact of radiotherapy and histological risk factors on outcomes in malignant phyllodes tumors

Abstract Purpose Breast phyllodes tumors (PT) are classified into benign, borderline and malignant grades based on histopathologic characteristics. Specific to malignant PT (MPT), surgery is the mainstay of the treatment yet relapse rates are high and knowledge gaps in the literature exist regarding the role of adjuvant radiotherapy (RT). We aimed to investigate the outcomes of malignant PT (MPT) patients treated in a tertiary Asian institution. Methods and materials Newly diagnosed non-metastatic MPT treated from February 1992 to June 2019 were analyzed retrospectively. RT details and relapse fields were analyzed. Outcomes of both groups (with and without adjuvant RT) were compared using log-rank test and hazard ratios were calculated using Cox proportional hazard test. Multivariable analysis was performed. Results Twenty-two out of 89 patients received adjuvant RT and the median dose was 60Gy in 30 fractions. In the no-RT group, 4 patients received RT upon relapse and had no further recurrences after; a further 2 received RT for fungating local relapse with good symptomatic relief. RT was only increasingly prescribed after 2004. Median follow-up in the RT group was 3.31 years, compared to 6.17 years in the no-RT group. In the RT group, 15 patients (68.2%) underwent mastectomy, vs 39 (58.2%) in the no RT group. One patient in the RT group developed an infield local relapse, compared to 21 out of 67 patients in the no-RT group. Multivariate model showed that RT decreased risk of locoregional failure (HR 0.12, 95%CI 0.02-0.92, p=0.04). Three-year LRFS was higher in the RT group, 92.3% (95%CI 78.9-100) vs 73.3% (95%CI 63.1-85.1) in the no-RT group (p=0.03). There were no differences in 3-year distant disease-free survival and overall survival. Conclusions We recommend that adjuvant radiotherapy be discussed for malignant phyllodes tumors for local control, even after mastectomy.